Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal inkjet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
Supplying ink from an ink reservoir to many thousand densely packed nozzles is a particular challenge in high-resolution pagewidth printing. One problem is avoiding ink pressure surges when a nozzle stops printing. During printing, each nozzle acts like a pump so that each nozzle chamber is refilled with ink almost instantaneously. Forming the nozzle chambers from hydrophilic materials (e.g. silicon nitride, silicon dioxide etc.) facilitates refilling of nozzle chambers during printing.
However, when printing ceases, it is equally important that ink does not flood out from nozzle openings and onto the printhead face. Flooding of this nature has a deleterious effect on print quality and may require frequent cleaning by a printhead maintenance station. Flooding is a particular problem in high-speed pagewidth printheads, where a relatively large mass of ink moves towards each nozzle of the printhead during printing. This moving mass of ink has an associated inertia, which may cause ink to continue leaking from nozzles even when printing ceases. The greater the momentum of ink in the ink supply system, the higher the risk of flooding.
To this end, pressure dampening structures have been proposed in the ink supply system, which absorb the pressure wave of ink being supplied to the nozzles. Hitherto, the Applicant has described air boxes in fluid communication with ink supply lines, which have a dampening effect on ink pressure waves. For a full discussion of ink pressure dampening, reference is made to [INSERT CROSSREF], the contents of which is herein incorporated by cross-reference. Essentially, it is desirable to allow some ‘give’ in the ink supply system, so that the pressure wave associated with a moving body of ink can be absorbed when printing ceases.
However, the use of air to absorb pressure surges is not wholly satisfactory. Outgassing of ink is a particular problem with air-dampening structures. Outgassing is undesirable, because air bubbles in the ink can lead to blockages in ink supply lines, and even initiate catastrophic printhead depriming. Furthermore, air-dampening structures are usually incorporated into ink supply systems a relatively long distance upstream of the inkjet nozzles—typically in a molded ink manifolds to which a MEMS printheads is mounted. Any ink downstream of such air-dampening structures will still carry a significant momentum that will not be absorbed by the air-dampening structures. Again, this problem is exacerbated in pagewidth printheads, which carry a large volume of ink compared to traditional scanning printheads.
It would be desirable to provide improved dampening structures, which are capable of absorbing pressure surges in ink supplied to inkjet nozzles. In view of the problems of outgassing, it would desirable to avoid air dampening as a means for dampening pressure surges. It would be further desirable to minimize the mass of ink between the dampening structures and the inkjet nozzles so as to improve the efficacy of any dampening system.